<select name="horarioTrabajo">
  <option value=""></option>
  <option value="Matutino" <? if($horario == "Matutino") echo "SELECTED";?>>Matutino</option>
  <option value="Vespertino" <? if($horario == "Vespertino") echo "SELECTED";?>>Vespertino</option>
  <option value="Completo" <? if($horario == "Completo") echo "SELECTED";?>>Completo</option>
</select>